WO2016163592A1 - Reinforced transparent composite material and manufacturing method therefor - Google Patents

Abstract

The present invention relates to: a reinforced transparent composite material comprising a hydrophobic nano-fiber sheet; and a manufacturing method therefor.

Description

Reinforced transparent composite material and its manufacturing method

The present invention relates to a reinforced transparent composite material including a hydrophobic nanofiber sheet and a manufacturing method thereof.

Glass is transparent, strong, and has a low coefficient of thermal expansion, so it is used throughout the real life and industry, but has a fatal disadvantage of being easily broken. Optical materials to replace glass include various optical plastics such as PC (polycarbonate), PMMA (polymethyl methacrylate) and PET (polyethylene terephthalate), but they are not as strong as glass, easily deformed, and have poor thermal stability. There is a limit to replacing glass.

To supplement the shortcomings of optical plastics, glass fiber reinforced transparent composite materials reinforced with transparent glass fiber reinforced materials have been developed. It has been spotlighted as an alternative to glass due to its strength and low thermal expansion rate, but has a disadvantage in that it is difficult to accurately match the refractive index of glass fiber and transparent resin in the visible light range and poor turbidity characteristics due to poor surface flatness. If the turbidity is not good, there is a limit to use as an optical material because the transmitted light is spread.

Recently, research using cellulose fibers of nano-diameter, not glass fibers, as a reinforcing material for transparent composite materials has been conducted. Nanofibers are as strong and transparent as glass, and because the fiber diameter (<100 nm) is much smaller than the wavelength of visible light (400-800 nm), the light is hardly recognized by the fiber. And turbidity). In addition, since the cellulose has a low coefficient of thermal expansion, the composite material based thereon can also reduce the coefficient of thermal expansion similar to glass by cellulose, which can be significantly improved compared to plastics in terms of thermal stability.

To date, composite materials using nanofibers have been made thinner to 100 μm or less to produce transparent films, or thicker than several millimeters to produce plates with high strength. However, it has been pointed out that the former is too thin in order to secure transparency, the strength is low, and the latter is optically opaque.

There are two methods for producing such a conventional nanofiber-reinforced composite material. The first method is to produce nanofibers by dispersing the nanofibers in a transparent resin and then heat or photocuring the second method. .

The first method is that the nanofibers have a fiber diameter of 100 nm or less, so that the surface area is large in volume and the nanofibers are irregularly arranged in the transparent resin, so that a large amount of fibers cannot be added. Therefore, it is possible to obtain a transparent composite material, but the strength was not high because the reinforcing effect by the nanofiber is not large.

The second method is to form a nanofiber sheet through the process of filtering the nanofiber aqueous dispersion solution, which is likely to occur when the water is removed and dried, the nanofibers are bonded to each other, resulting in a larger fiber size Closed pores can form between the fibers. Therefore, in the impregnation process of infiltrating the transparent resin into the sheet, it becomes difficult to enter the transparent resin and the fiber size becomes 100 nm or more, resulting in a problem of deterioration of optical properties.

Accordingly, there is a continuing need for transparent composite materials having high strength and high transparency, which have excellent impact resistance to replace glass in technical fields such as electronic device displays, automobile glass, and window glass, and have improved optical characteristics.

It is an object of the present invention to provide a reinforced transparent composite material comprising a hydrophobic nanofiber sheet.

Still another object of the present invention is to provide a method for producing the reinforced transparent composite material including a hydrophobic nanofiber sheet.

In order to achieve the above object, the reinforced transparent composite material according to an embodiment of the present invention includes a hydrophobic nanofiber sheet.

The hydrophobic nanofibers may have a surface tension of 40 to 70 mN / m based on 1 wt% aqueous solution.

The hydrophobic nanofibers can be derived from plants.

The plants are lovegrass, bamboo, silver maple tree, tulip tree, trident maple, rice, lotus and pyracantha. It may be one or more selected from the group consisting of.

The plant may be bamboo.

The hydrophobic nanofibers may have a diameter of 5 to 100 nm.

The hydrophobic nanofiber sheet may have a thickness of 20 to 1,000 μm.

The reinforced transparent composite material may include two or more hydrophobic nanofiber sheets.

The reinforced transparent composite material may have a thickness of 0.2 to 1.5 mm.

Method for producing a reinforced transparent composite material according to another embodiment of the present invention comprises the steps of (i) preparing a hydrophobic nanofiber sheet; (ii) impregnating the hydrophobic nanofiber sheet into the transparent resin; And (iii) molding the impregnated hydrophobic nanofiber sheet.

Step (ii) may involve heating.

The transparent resin may have a viscosity of 100 to 10,000 cps.

Step (iii) may be carried out by thermal curing.

Step (iii) may involve pressurization.

Step (iii) may further comprise a drying step before molding.

Step (ii) may further comprise impregnating and stacking two or more hydrophobic nanofiber sheets.

In the above method, the hydrophobic nanofibers may have a surface tension of 40 to 70 mN / m based on 1 wt% aqueous solution.

In the method, the hydrophobic nanofiber may be derived from a plant.

In the method, the plants are lovegrass, bamboo, silver maple tree, tulip tree, trident maple, rice, lotus and blood It may be at least one selected from the group consisting of pyracantha.

In the method, the plant may be bamboo.

In the method, the hydrophobic nanofibers may have a diameter of 5 to 100 nm.

In the above method, the hydrophobic nanofiber sheet may have a thickness of 20 to 1,000 μm.

Hereinafter, the present invention will be described in more detail.

In one embodiment, the reinforced transparent composite material of the present invention comprises a hydrophobic nanofiber sheet. The present invention relates to a reinforced transparent composite material, and more particularly to a reinforced transparent composite material produced by impregnating a transparent resin after the sheet is made of nanofibers having a hydrophobicity.

The present invention is to obtain a nanofiber for reinforcing the material using a plant-derived fiber raw material, in particular, using plants having hydrophobic properties to reduce the aggregation phenomenon of the nanofiber by hydrogen bonding, which causes closed pores during the nanofiber sheet forming process It was conceived that it is possible to secure pores through which transparent resin can penetrate.

Nanofibers are easily deformed because of their small cross-sectional secondary moments and are also very cohesive and generally have poor compatibility with resins. Therefore, the process of suppressing the aggregation of the nanofibers is essential, and there is a need to find a way to sufficiently and uniformly penetrate the transparent resin into the fine pores between the fibers. In addition, in the method of manufacturing a transparent composite material, using a method of forming a nanofiber sheet and impregnating it into a transparent resin, without dispersing the nanofibers themselves in a transparent resin, a larger amount of fiber is added to This method is preferred because the reinforcing effect can be greatly seen. However, when using a plant-derived nanofiber as a material, the cellulose aqueous dispersion solution is filtered to form a nanofiber sheet. Hydroxyl groups (-OH) have strong hydrogen bonds, and the phenomenon of nanofibers is frequently combined. This causes the fibers to increase in size and create closed pores between the fibers. As a result, in the impregnation process of infiltrating the transparent resin into the sheet, it becomes difficult to infiltrate the transparent resin, and when the combined fiber size is 100 nm or more, a problem of deterioration of the optical properties occurs.

In the molecular structure, cellulose has surface anisotropy along the polymer chain with hydroxyl groups on the side and hydrocarbon groups on the upper and lower sides, hydrophilicity on the side, and hydrophobicity on the upper and lower sides (FIG. 1). Plant-derived nanofibers are formed in a crystal structure in which cellulose molecules are arranged, and the size of hydrophobicity or hydrophilicity varies according to the arrangement structure. Here, hydrophobicity and hydrophilicity are relative concepts. As hydrophobicity increases, hydrophilicity decreases. In the case of nanofibers in which cellulose molecules are arranged in a rhombus shape, relatively hydrophilicity is revealed on the surface, so that the hydrophilicity becomes hydrophilic. In the case of the arrangement, the upper and lower hydrophobic surfaces are exposed on the surface of the nanofibers to show hydrophobicity (FIG. 1). These hydrophilic / hydrophobic properties can be compared relatively by measuring the surface tension of the plant-derived nanofiber aqueous solution.

In general, since plant-derived cellulose fibers have been widely used in the papermaking field, hardwoods or conifers, which have low manufacturing costs, have been used, and nanofibers have been produced mainly from hardwoods or conifers. However, according to the measurement results of the surface tension of the 1% by weight nanofiber solution as shown in Table 1, the surface tension of bamboo nanofibers was lower than that of softwood and hardwood.

	Bamboo Nanofiber Aqueous Solution	Hardwood nanofiber aqueous solution	Coniferous Nanofiber Solution
Surface tension * (mN / m)	59.11	72.33	81.08

It can be seen from the surface tension measurement result that bamboo has a hydrophobicity with low affinity with water relative to conifers or hardwoods. When the nanofiber sheets produced using bamboo, hardwood and conifer nanofibers were observed through an electron microscope, the surface shape difference could be observed. In the order of hydrophobicity, the hydrophobicity decreased gradually in the order of bamboo, hardwood and softwood nanofibers. In particular, in the case of bamboo nanofibers, the bonds between the fibers are small and the pores between the fibers are maintained (FIG. 2).

Therefore, when the nanofiber sheet is manufactured using plant-derived natural cellulose nanofibers showing hydrophobicity as in the present invention, since the cellulose molecules have a relatively high fraction of blocks arranged in a block form, the hydrophilic side that exposes the hydroxyl group is hidden. The highly hydrophobic upper and lower surfaces are exposed on the surface of the nanofibers, thereby preventing hydrogen bonding, preventing aggregation between the nanofibers, and as a result, the nanofiber sheets can maintain open pores (FIG. 2). That is, the reinforced transparent composite material including the hydrophobic nanofiber sheet of the present invention includes nanofibers in the form of a sheet, while securing its strength, and particularly including hydrophobic nanofibers, conventional plant-derived cellulose nanofiber sheets such as conifers and hardwoods. Solving the problem of the closed pores that have had, through the open pores of the sufficiently secured sheet is very easy to penetrate the transparent resin can significantly improve the optical properties of the material. The nanofiber-reinforced transparent composite material including the hydrophobic nanofiber sheet according to the present invention may exhibit a transmittance of 90% or more and a haze of less than 1% even when manufactured to a thickness of 1 mm or more, and has higher impact resistance and tensile strength than glass. The mechanical strength is improved.

As described above, the reinforced transparent composite material of the present invention may be implemented through a method of forming a nanofiber sheet and impregnating it in a transparent resin. The transparent resin usable in the present invention can be used without limitation as long as it is a resin commonly used in transparent composite materials, such as acrylic resins, methacryl resins, epoxy resins, urethane resins, olefin resins, phenol resins, melamine resins and novolac resins. , Urea resin, guanamine resin, alkyd resin, unsaturated polyester resin, vinyl ester resin, diallyl phthalate resin, silicone resin, furan resin, ketone resin, xylene resin, thermosetting polyimide, styrylpyridine resin, tria Tactile resin etc. are mentioned. Among these, an epoxy resin, a silicone resin, an acrylic resin, and a methacryl resin with high transparency may be preferable. These transparent resins may be used individually by 1 type, and may mix and use 2 or more types.

In a particular embodiment, the transparent resin may be a thermoplastic resin or a thermosetting resin.

The content ratio of the reinforcing material in the transparent composite material of the present invention, that is, the content ratio of the hydrophobic nanofiber sheet may be 5 to 60% by weight, preferably 10 to 40% by weight, more preferably 10 to 30% by weight. By setting the content ratio of the reinforcing material to 5% by weight or more, it is possible to obtain the effect of improving the mechanical strength, reducing the coefficient of thermal expansion, and improving the modulus of elasticity at high temperature, and by setting it to about 60% by weight or less, the transmittance of the transparent composite material. Effects such as reduction inhibition, turbidity increase suppression, and a decrease in moisture absorption can be obtained.

In certain embodiments, the transparent composite material of the present invention may contain one or more additives at a level that does not impair the transparency of the material and the effects of the present invention. Specific examples of the additive include compatibilizers such as maleic anhydride and modified polypropylene; Surfactants; Polysaccharides such as starch and alginic acid; Natural proteins such as gelatin glue and casein; Inorganic compounds such as tannins, zeolites, ceramics, and metal powders; coloring agent; Plasticizers; Spices; Pigments; Rheology modifiers; Leveling agents; Conducting agents; Antistatic agents; Ultraviolet absorbers; UV dispersants; Deodorant and the like, but is not limited thereto. When using such an additive, you may use individually by 1 type, and can also mix and use 2 or more types.

The refractive index of the transparent resin contained in the transparent composite material of the present invention may be in the range of 1.53 to 1.59, in this range can be obtained a transparent composite material particularly close to the flexural speed of the plant fiber. Since the refractive index of the hydrophobic nanofibers of the present invention may range from 1.54 to 1.58, matching the refractive indexes of the hydrophobic nanofibers and the transparent resin may increase the transmittance and reduce turbidity.

In a particular embodiment, the nanofiber sheet included in the reinforced transparent composite material of the present invention may have a surface tension of the hydrophobic nanofibers constituting the sheet 40 to 70 mN / m based on 1% by weight aqueous solution. Preferably the surface tension of the hydrophobic nanofibers may be 45 to 65 mN / m, more preferably 50 to 60 mN / m. By setting the surface tension of the hydrophobic nanofibers to 40 mN / m or more, while maintaining open pores in the nanofiber sheets, hydrogen bonds are formed at the overlapping portions of the nanofibers to form a net-like structure to improve mechanical strength and elastic modulus. This is because the effect of the improvement can be obtained, and the permeability of the hydrophobic transparent resin to the nanofiber sheet can be improved by setting it at 70 mN / m or less, so that the transmittance of the transparent composite material can be improved and the turbidity improvement can be obtained.

In a specific embodiment, the raw material of the nanofibers used in the reinforced transparent composite material according to the present invention is good bamboo, the surface tension of the bamboo-derived nanofibers based on 1% by weight aqueous solution is 40 to 70 mN / m, Specifically, it may be 45 to 65 mN / m.

In certain embodiments, the hydrophobic nanofibers can be derived from plants. The plants are lovegrass, bamboo, silver maple tree, tulip tree, trident maple, rice, lotus and pyracantha. It may be one or more selected from the group consisting of. As described above, the reinforcing transparent composite material of the present invention includes a sheet containing hydrophobic nanofibers, and therefore, any of the leaves of the plant exhibiting the desired hydrophobicity can be used. The desired hydrophobicity in the reinforced transparent composite material of the present invention is that the surface tension of the aqueous solution of nanofibers based on 1% by weight aqueous solution as described above can be measured to 40 to 70 mN / m. Particularly preferably, the plant may be bamboo.

In certain embodiments, the nanofibers making up the hydrophobic nanofiber sheet may have a diameter of 5 to 100 nm. Specifically the nanofibers may have a diameter of 10 to 60 nm, more preferably 20 to 40 nm. When the diameter of the nanofibers is 5 nm or more, it is possible to increase the nanofiber content when manufacturing the transparent composite material by suppressing the increase of the pores in the nanofiber sheet so that the effect of improving the mechanical strength and the elastic modulus can be obtained. If the wavelength is less than 100 nm, the visible light may not recognize the nanofibers well, thereby obtaining excellent optical properties (transmittance and turbidity) of the transparent composite material. In other words, when a fiber having a diameter larger than the wavelength of the visible ray is basically combined with a transparent resin as a reinforcing material, visible light scattering occurs, resulting in a problem that the transparency of the resin is impaired. It can be set in the range of 5 to 100 nm so that the nanofibers can usefully function as a material for reinforcing the transparent resin.

In a particular embodiment, the hydrophobic nanofiber sheet included in the reinforced transparent composite material of the present invention may have a thickness of 20 to 1,000 μm. Preferably the hydrophobic nanofiber sheet may have a thickness of 30 to 500 μm, more preferably 50 to 200 μm. By setting the thickness of the nanofiber sheet to 20 μm or more to prevent the sheet thickness is broken or deformed by the thermal process when manufacturing the composite material, by setting it to 1,000 μm or less, the sheet has a uniform density in the thickness direction and transparent resin This is because it is easy to penetrate to the inside of the sheet, and thus the effect of improving the transmittance and turbidity of the composite material can be obtained.

In certain embodiments, the reinforced transparent composite material of the present invention may comprise two or more hydrophobic nanofiber sheets. By stacking two or more hydrophobic nanofiber sheets to form a reinforced transparent composite material, the thickness and strength can be adjusted to be suitable as target components.

In certain embodiments, the reinforced transparent composite material of the present invention may have a thickness of 0.2 mm to 1.5 mm. Preferably the thickness of the reinforced transparent composite material may be 0.4 mm to 1.0 mm, more preferably 0.5 mm to 0.7 mm. This is because by setting the thickness of the reinforced transparent composite material to 0.2 mm or more, it is possible to prevent breakage because the thickness is thin, and to replace the glass used in the thin electronic device by setting it to 1.5 mm or less.

Method for producing a reinforced transparent composite material according to another embodiment of the present invention comprises the steps of (i) preparing a hydrophobic nanofiber sheet; (ii) impregnating the hydrophobic nanofiber sheet into the transparent resin; And (iii) molding the impregnated hydrophobic nanofiber sheet.

The step (i) preparing the hydrophobic nanofiber sheet begins with the process of unpacking the cellulose fibers in the dry plant fibers and decomposing them to nanofiberize a portion of the plant fibers. At this time, it is preferable that the average fiber diameter is resolved to about 5 to 200 μm to obtain appropriate freeness. As a method for decomposing plant fibers, a known method may be employed. For example, a method of decomposing and dissolving a water suspension of a raw material containing the cellulose fibers and a slurry by mechanically grinding a refiner using a refiner high pressure homogenizer, grinder, bead mill, or the like may be employed. Method can be used. Alternatively, raw fiber leaves may be mechanically dehydrated in a dry state to obtain nanofibers. The moisture content of the raw material may be at least 3% by weight, preferably at least 4% by weight, and more preferably at least 5% by weight. If the moisture content of the raw material is too small, the cellulose fibers may be in close proximity to each other and the hydrogen between the cellulose fibers may be reduced. The sea islands become insufficient because the bonding develops and the mechanical sea island effect can be reduced.

Although the shaping | molding method is not specifically limited in order to form a sheet | seat from aqueous nanofiber solution, The method of pressure-reducing filtering or pressure-filtering the nanofiber aqueous solution slurry obtained through the said island fiber process, for example by a suction filtration filter can be used. After filtering, it may be molded into a sheet through additional processes such as drying, heat compression, and the like. The drying process may be performed at 100 to 150 ° C. In order to evaporate water, a temperature of 100 ° C. or higher is required, and nanofibers may be damaged by heat at a temperature of 150 ° C. or higher.

Thereafter, the nanofiber sheet is impregnated in the transparent resin (step (ii)), the transparent resin used at this time is as described above for the reinforced transparent composite material of the present invention. Step (ii) may involve heating.

The viscosity of the transparent resin may be 100 to 10,000 cps, preferably 200 to 7,000 cps, more preferably 250 to 5,000 cps. In particular, in order to penetrate well between pores between nanofibers, the viscosity is preferably 10,000 cps or less, and when heat is applied at 60 to 90 ° C. during impregnation, the viscosity of the transparent resin may be reduced to enhance penetration between pores. When the viscosity is 100 cps or less, the transparent resin does not stay in the nanofiber sheet when heated, and easily exits, so that the composite material becomes opaque. Through the impregnation process, the nanofiber sheet becomes transparent. It is important to sufficiently infiltrate the transparent resin between the nanofibers. Therefore, this impregnation step can be carried out in part or in whole while changing the pressure, and a method of changing the pressure may be reduced pressure or pressure. When the pressure is reduced or pressurized, the air present between the nanofibers can be easily replaced with the above-mentioned transparent resin, and the remaining of bubbles can be prevented.

Thereafter, the impregnated nanofiber sheet is subjected to a forming step (step (iii)), which is a process of curing the nanofiber sheet impregnated with the transparent resin. This curing process may be performed by a polymerization reaction, a crosslinking reaction, a chain extension reaction, or the like. In addition, it may be made of a method of removing the solvent in the transparent resin. The solvent removal may include evaporation removal under reduced pressure as well as evaporation removal under atmospheric pressure.

In this case, step (iii) may be performed by conventional curing of a transparent composite material such as curing by heating / cooling or photocuring, but is not limited thereto. In particular, the forming step may be performed by thermosetting, and may involve pressurization. For example, the sheet may be pressurized thermoformed by hot press. At this time, when impregnated with two or more hydrophobic nanofiber sheets in the step (ii), it is possible to obtain a transparent composite material whose thickness can be adjusted to be suitable as the target component in this step (iii). The pressure applied during thermoforming is preferably 100 to 600 MPa, and if the pressure is too low, the gap between the pores in the sheet or the laminated sheets is widened, and thus it is difficult to obtain uniform characteristics. The heat treatment condition is preferably at least 2 hours at 100 to 170 ° C, because when the transparent resin is cured at 100 ° C or more and the heat treatment temperature is too high, damage may occur to the nanofibers and the transparent resin, thereby causing discoloration. In addition, by fixing the nanofiber entanglement by the thermal pressure treatment, the effect of reducing the coefficient of thermal expansion and improving the Young's modulus of the transparent composite material can be expected.

In certain embodiments, step (iii) may further comprise a drying step prior to molding.

In a particular embodiment, the hydrophobic nanofibers used in the method may have a surface tension of 40 to 70 mN / m based on 1% by weight aqueous solution. Preferably the surface tension of the hydrophobic nanofibers may be 45 to 65 mN / m, more preferably 50 to 60 mN / m. By setting the surface tension of the hydrophobic nanofibers to 40 mN / m or more, while maintaining open pores in the nanofiber sheets, hydrogen bonds are formed at the overlapping portions of the nanofibers to form a net-like structure to improve mechanical strength and elastic modulus. This is because the effect of the improvement can be obtained, and the permeability of the hydrophobic transparent resin to the nanofiber sheet can be improved by setting it at 70 mN / m or less, so that the transmittance of the transparent composite material can be improved and the turbidity improvement can be obtained.

In certain embodiments, the hydrophobic nanofibers used in the method may be derived from plants.

In a particular embodiment, the plant used in the method is lovegrass, bamboo, silver maple tree, tulip tree, trident maple, rice, It may be at least one selected from the group consisting of lotus and pyracantha. As described above, the reinforced transparent composite material of the present invention includes a sheet containing hydrophobic nanofibers, and accordingly, any of the leaves of the plant showing the desired hydrophobicity can be used in the above method. The desired hydrophobicity in the reinforced transparent composite material of the present invention prepared by the above method is that the surface tension of the aqueous solution of nanofibers can be measured at 40 to 70 mN / m based on 1 wt% aqueous solution as described above.

In certain embodiments, the plant used in the method may be bamboo.

In certain embodiments, the hydrophobic nanofibers used in the method may have a diameter of 5 to 100 nm in diameter. Specifically the nanofibers may have a diameter of 10 to 60 nm, more preferably 20 to 40 nm. When the diameter of the nanofibers is 5 nm or more, it is possible to increase the amount of nanofibers in the production of the transparent composite material by suppressing the excessive pore in the nanofiber sheet, thereby improving the mechanical strength and elastic modulus of the transparent composite material obtained by the above method. This is because it is possible to obtain an effect of improving the optical properties, and if it is 100 nm or less, visible light does not recognize the nanofibers well so that excellent optical properties (transmittance and haze) of the transparent composite material can be obtained. In other words, when a fiber having a diameter larger than the wavelength of the visible ray is basically combined with a transparent resin as a reinforcing material, visible light scattering occurs, resulting in a problem that the transparency of the resin is impaired. It can be set in the range of 5 to 100 nm so that the nanofibers can usefully function as a material for reinforcing the transparent resin.

In certain embodiments, the hydrophobic nanofiber sheet used in the method may have a thickness of 20 to 1,000 μm. Preferably the hydrophobic nanofiber sheet may have a thickness of 30 to 500 μm, more preferably 50 to 200 μm. By setting the thickness of the nanofiber sheet to 20 μm or more to prevent the sheet thickness is broken or deformed by thermal process during the execution of the transparent composite material manufacturing method of the present invention, by setting the thickness of less than 1,000 μm in the thickness direction This is because the transparent resin can easily penetrate the inside of the sheet with a uniform density, and the effect can be obtained for improving the transmittance and turbidity of the transparent composite material obtained by the above method.

The present invention is to provide a reinforced transparent composite material, and more particularly, to a transparent composite material prepared by impregnating and molding a transparent resin after producing a hydrophobic nanofiber sheet and a method for producing the same. According to the present invention, since the nanofiber composite material is transparent and resistant to breakage compared to glass, the front cover of the mobile device display, the front cover of the flexible device, the window glass of a transport device such as a car, a train, a ship, an airplane, a camera, and a camcorder play a video. Internal parts such as lenses such as devices, printing devices, copying devices, building materials, organic EL displays, organic EL displays, and glass substrates, touch panels, transparent parts for headlights, etc. It is possible to use in place of.

According to the present invention, it is possible to solve the conventional problem that it is difficult to maintain strong and transparent optical properties at the same time in the production of nanofiber-reinforced composite material, which can significantly improve the strength and optical properties of the nanofiber transparent composite material at the same time. have. The reinforced transparent composite material according to the present invention exhibits transmittance and turbidity <1% of 90% or more at a thickness of 1 mm. In addition, since the plant-derived fiber is used as the reinforcing material, the glass fiber is used as a reinforcing material, and thus, the transparency is maintained and the specific gravity is low according to the temperature change.

1 is a conceptual diagram illustrating the hydrophilic / hydrophobic characteristics of plant leaves according to the molecular structure and cellulose molecular arrangement of the cellulose.

Figure 2 is an electron micrograph of the surface shape of the nanofiber sheet according to the plant fiber raw material.

3 is a manufacturing process chart of the reinforced transparent composite material of the present invention according to one embodiment.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Example 1

1. Preparation of Nanofiber Sheets

Bamboo pulp fibers were repeatedly grindized with a grinder (Super Masscolloider, Masuko Sangyo Co., Ltd.) at least 60 times to prepare bamboo nanofibers, and diluted with water to adjust the concentration to 1% by weight. The diluted solution was treated with a homogeneous mixer (T18 basic ULTRA-TURRAX, IKA) for 10,000 rpm for 3 minutes, and then treated with an ultrasonic homogenizer (VC505 Vibra cell, SONICS) at 30% output for 30 minutes to uniformly dispersed aqueous nanofiber solution. Got it. Spin coating (3,000 rpm, 30 seconds) the aqueous nanofiber solution onto the silicon substrate and using a scanning electron microscope (SEM) and atomic force microscope (AFM) to confirm that the nanofiber diameter is 100 nm or less. Could. In addition, the nanofiber aqueous solution was measured with a surface tension meter (DSA100, KRUSS) as a result of confirming the surface tension of 59.11 mN / N. Polyvinylidene fluoride (PVDF) filter and reduced pressure filter system (ADVENTEC) were used to prepare nanofiber sheets, and 80 ml aqueous solution was filtered and dried at 100 ° C. for 1 hour to obtain a sheet having a thickness of about 100 μm.

2. Manufacturing of transparent resin

Bisphenol A epoxy (Bisphenol A diglycidyl ether, KDS8128, Kukdo Chemical), anhydrous curing agent (Methylhexahydrophthalicanhydride, KFH271, Kukdo Chemical), low viscosity diluent (3-ethyl-3-hydroxymethyl-oxetane, OXT-101, Toagosei) After mixing to 110: 15, 2-? Ethyl-? 4-? Methylimidazole (sigma aldrich) was added as an initiator to 0.15 wt% of the weight of the transparent resin to prepare a transparent resin. The transparent resin was cured by maintaining at 90 ° C. for 2 hours and then heating at 150 ° C. for 2 hours. When the cured product was measured with a refractive index meter (AR2008, KRUSS), a refractive index of 1.54 was obtained.

3. Manufacture of transparent composite material

In order to infiltrate the transparent resin into the pores between the nanofibers, the nanofibers were immersed in the transparent resin solution and placed in a vacuum oven (OV11, Zeotech) and then decompressed to 0.1 MPa at 70 ° C. and maintained for 2 hours. Seven sheets of resin-infiltrated nanofiber sheets were laminated, inserted into a mold capable of producing a plate having a thickness of 1 mm, and heated at 150 ° C. for 3 hours with a pressure of 30 MPa using a thermocompressor to prepare a reinforced transparent composite material. . The content of the nanofibers in the prepared composite material was 10.88% by weight.

Comparative Example 1

The composite material was prepared by treating the hardwood pulp in the same manner as in Example 1, but seven nanofiber sheets were used in the same manner. There was no.

Comparative Example 2

The composite material was prepared by treating the coniferous pulp in the same manner as in Example 1, but seven nanofiber sheets were used in the same manner, but since the permeability of the transparent resin decreased, a large number of pores existed in the composite material to calculate the nanofiber content. There was no.

Property evaluation

Composites prepared through the Examples and Comparative Examples were measured for transmittance and turbidity at a wavelength of 360 ~ 740 nm by using Spectrophotometer CM-5 of KONICA MINOLTA, and three points by ASTM D790 measurement standard using UTA500 of Jindong Corporation Flexural strength was measured. The results are shown in Table 2 below.

	Bamboo Nanofiber	Hardwood Nano Fiber	Conifer nanofiber
Resin penetration	O	X	X
Transmittance (%)	91.2	79.4	57.0
Turbidity (%)	0.6	27.1	60.2
Flexural Strength (MPa)	261	112	43

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (22)

1. Reinforced transparent composite material comprising a hydrophobic nanofiber sheet.
2. The reinforced transparent composite material of claim 1, wherein the hydrophobic nanofibers have a surface tension of 40 to 70 mN / m based on a 1 wt% aqueous solution.
3. The reinforced transparent composite material of claim 1, wherein the hydrophobic nanofibers are plant derived.
4. 4. The plant of claim 3 wherein the plant is aged in lovegrass, bamboo, silver maple tree, tulip tree, trident maple, rice, lotus and Reinforced transparent composite material that is at least one selected from the group consisting of pyracantha.
5. The reinforced transparent composite material of claim 3, wherein the plant is bamboo.
6. The reinforced transparent composite material of claim 1, wherein the hydrophobic nanofibers have a diameter of 5 to 100 nm.
7. The reinforced transparent composite material of claim 1, wherein the hydrophobic nanofiber sheet is 20 to 1,000 μm thick.
8. The reinforced transparent composite material of claim 1, comprising two or more hydrophobic nanofiber sheets.
9. The reinforced transparent composite material of claim 8, wherein the thickness is 0.2 to 1.5 mm.
10. (i) preparing a hydrophobic nanofiber sheet;

    (ii) impregnating the hydrophobic nanofiber sheet into the transparent resin; And

    (iii) forming the impregnated hydrophobic nanofiber sheet

    Method for producing a reinforced transparent composite material comprising a.
11. The method of claim 10, wherein step (ii) involves heating.
12. The method of claim 10, wherein the transparent resin has a viscosity of 100 to 10,000 cps.
13. The method of claim 10, wherein step (iii) is performed by thermosetting.
14. The method of claim 10, wherein step (iii) involves pressurization.
15. The method of claim 10, wherein step (iii) further comprises a drying step prior to molding.
16. The method of claim 10, wherein step (ii) further comprises impregnating and stacking two or more hydrophobic nanofiber sheets.
17. The method of claim 10, wherein the hydrophobic nanofibers have a surface tension of 40 to 70 mN / m based on a 1 wt% aqueous solution.
18. The method of claim 10, wherein the hydrophobic nanofibers are plant derived.
19. 19. The plant of claim 18, wherein the plant is aged in lovegrass, bamboo, silver maple tree, tulip tree, trident maple, rice, lotus and At least one selected from the group consisting of pyracantha.
20. The method of claim 18, wherein the plant is bamboo.
21. The method of claim 10, wherein the hydrophobic nanofibers are 5 to 100 nm in diameter.
22. The method of claim 10, wherein the hydrophobic nanofiber sheet is 20 to 1,000 μm thick.

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